If you want to keep your brain from shrinking as you age, your best bet may be to keep yourbody physically fit. New research from Boston University School of Medicine found that poor physical fitness in midlife was linked to smaller brain size (a sign of accelerated brain aging) 20 years later. Researchers used treadmill tests to assess the physical fitness of 1,583 people whose average age was 40. All were participants in the long-running Framingham (MA) Heart Study, and none had heart disease when they took their first treadmill test. They were re-evaluated with treadmill tests two decades later and also underwent MRI scans of their brains. Results showed that the poorer the participants performed on their original treadmill tests, the more volume their brains had lost over the 20 years. The researchers also reported that the higher an individual’s blood pressure and heart rate rose during the first treadmill test - changes that could mean lack of fitness - the smaller their brains were likely to be on the MRI scans 20 years later. The study doesn’t prove that poor physical fitness caused the brain shrinkage observed, but does suggest an association.